This invention concerns a mill for removing a packer from an oil well or the like.
A packer is a device placed in the steel casing of an oil well for isolating upper and lower sections of such casing. In a dual string packer there are two non-axial bores and surrounding structure that seals the packer inside the casing. Tubing can be connected to or through the packer for injecting and/or withdrawing fluids from the well. A broad variety of packers are commercially available and the structure thereof is of no significance for this invention.
Some dual string packers are designed for release so that they can be readily removed from the casing and others are more or less permanently fixed in the casing. Even with the readily removable packers it often occurs that corrosion or the like prevents removal. Thus, it is not an uncommon procedure in work-over of oil wells to require milling of the packer to remove it from the well. Such milling destroys the packer and milling chips are pumped out of the well or are caught in downhole debris collectors. Junk that remains in the well can be removed with a magnet or can be milled by a conventional junk mill.
As milling of a packer continues a point is ordinarily reached where the remains of the packer and any tubing or the like hanging from it are freed from the casing and may fall free. A packer mill for single completion packers has a grip or catcher on the milling tool used to mill the packer that catches the remains of the milled packer so that they can be drawn upwardly and removed from the well bore.
It sometimes occurs as the remains of the packer are lifted that they become stuck in the well bore. It may also occur that the milling tool becomes worn or damaged before the packer is free. In either of these circumstances it may be desirable to remove the milling tool while leaving the remainder of the packer in the well. It is therefore desirable to provide a means for releasing the packer mill from the packer. The mill can then be withdrawn and the well reentered with the same or a different tool for completing removal of the packer.
One novel approach for a single completion packer is disclosed in U.S. patent application Ser. No. 675,354 filed on Nov. 27, 1984, now U.S. Pat. No. 4,616,721, the subject matter of which is hereby incorporated by reference. This packer mill has a catcher sleeve with radially collapsible fingers which can pass through the bore of a single completion packer and expand once through the bore. When the packer is milled free, it falls to the catcher for lifting from the well. In the event the packer sticks in the well, the catcher can release by lifting hard. This causes bursting of a tension ring at the ends of the fingers. When the ring snaps, the catcher can contract, releasing the packer, and the packer mill can be withdrawn.
However, the packer mill of application No. 675,354 is a single completion packer mill that has a long catcher that extends below the central bore of the packer and supports the packer at the bottom. This mill and catcher cannot be used on a dual string packer which lacks a central bore. It is therefore desirable to provide a packer mill usable for a dual string packer, which will support the remains of the packer when freed in the well.
It is usual that the packer has the grips or locking sections that secure it in the well bore at or below the middle of the packer. When milling a stuck packer it does not ordinarily break free until at least a portion of the locking sectors have been milled. This means that much of the length of the packer must be milled at appreciable cost.
It is desirable to minimize the amount of the packer that is milled since the less metal removed by milling, the quicker the job can be completed. It is also important to remove the residual parts of the packer when less than all of it is milled since that is by far the most economical way to clean up the well.
It is also desirable to provide a means for releasing a packer mill from the remains of a packer that is stuck in the well with a high degree of reliability and without inherently producing loose parts that may cause further difficulty in the well bore.